a) Field of the Invention
The present invention relates to a solid-state image pickup device using charge-coupled devices (CCD), and in particular, to an interline transfer type solid-state image pickup device using CCD.
b) Description of the Related Art
After the CCD mass-producing technique has been established, image pickup devices such as an electronic still camera and a digital camera employing a solid-state image pickup device using CCD, particularly, an interline transfer type solid-state image pickup device using CCD have been rapidly developed and spread. In the description below, the solid-state image pickup device using CCD and conducting an interline transfer operation including a frame interline transfer operation will be simply referred to as xe2x80x9csolid-state image pickup devicexe2x80x9d.
A solid-state image pickup device includes, for example, a semiconductor substrate, a large number of photoelectric converter elements or photoelectric converters formed in one surface of the semiconductor substrate in a contour of an array having rows and columns, a vertical charge transfer element disposed for each column of the photoelectric converters, one horizontal charge transfer element electrically connected to the vertical charge transfer elements, and an output amplifier electrically connected to one end port of the horizontal charge transfer element.
The photoelectric converter is a photo diode in general, and the number of photoelectric converters ranges, for example, from about several hundreds of thousands to about several millions. In the known solid-state image pickup devices, the photoelectric converters are arranged in a pattern of a square matrix (also including a matrix of which the number of rows is not equal to that of the columns in this specification) or the photoelectric converters are arranged in a shifted-pixel layout.
In this specification, the shifted-pixel layout is an arrangement of the photoelectric converters in which each photoelectric converter of an even photoelectric converter column is shifted relative to an associated photoelectric converter of an odd photoelectric converter column by about one half of the pitch in the column direction. Similarly, each photoelectric converter of an even photoelectric converter row is shifted relative to an associated photoelectric converter of an odd photoelectric converter row by about one half of the pitch in the row direction. Each photoelectric converter column includes photoelectric converter of only odd or even rows. The shifted-pixel layout is a form of arrangement of a large number of photoelectric converters in a pattern of an array having rows and columns.
In this specification, xe2x80x9cabout one half of the pitch of the photoelectric converters in the photoelectric converter columnxe2x80x9d includes, in addition to one half of the pitch, any value which is different from one half of the pitch because of factors such as a manufacturing error and a rounding error of a pixel position appearing in a design phase or a mask fabrication process and which nevertheless can be regarded as substantially equivalent to one half of the pitch in consideration of obtained performance and picture quality of the solid-state image pickup device. This also applies to xe2x80x9cabout one half of the pitch of the photoelectric converters in the photoelectric converter rowxe2x80x9d.
Each vertical charge transfer element of the solid-state image pickup device is a CCD and includes one channel (to be referred to as xe2x80x9cvertical transfer channelxe2x80x9d hereinbelow) extending along an associated photoelectric converter column and many electrodes (to be referred to as xe2x80x9cvertical transfer electrodesxe2x80x9d hereinbelow) which cross the vertical charge transfer channel in a plan view. The vertical charge transfer channel is formed in a surface of the semiconductor substrate, and each vertical transfer electrode is formed on an electrically insulating layer disposed on the semiconductor substrate.
Ordinarily, one or two vertical transfer electrodes are disposed for one photoelectric converter row. Each vertical transfer electrode extends along an associated photoelectric converter row on an upstream side or a downstream side of the photoelectric converters of the row. Each photoelectric converter is surrounded by two vertical transfer electrodes, that is, by one upstream vertical transfer electrode and one downstream vertical transfer electrode in a plan view.
In this specification, movement of charge from photoelectric converters to the output amplifier is regarded as a flow, and a relative position of each constituent member or the like is identified as a position upstream of, for example, a unit A or a position downstream of, for example, a unit A according to necessity.
FIG. 7 schematically shows an example of layout of photoelectric converters and vertical transfer electrodes of a solid-state image pickup device of the prior art in a plan view. In this layout, a solid-state image pickup device 500 is a solid-state image pickup device of type in which a large number of photoelectric converters 510 are disposed in one surface of a semiconductor substrate 501 in the shifted-pixel layout.
One vertical transfer electrode 525 or 526 is formed for each photoelectric converter row. Each vertical transfer electrode 525 or 526 meanders along the associated photoelectric converter row on a downstream side thereof, generally extending in the direction of the photoelectric converter row. For a photoelectric converter row immediately on the downstream side of the vertical transfer electrode 525 or 526, the electrode 525 or 526 meanders along the photoelectric converter row on an upstream side thereof. Each photoelectric converter 510 is surrounded by two vertical transfer electrodes 525 and 526, one electrode is disposed on the upstream side of the converter 510 and the other electrode is disposed on downstream side of the converter 510 as described above.
In the solid-state image pickup device, electric charge accumulated in a photoelectric converter by photoelectric conversion is read out to an associated vertical charge transfer element. To control the readout operation of charge from the photoelectric converter to the vertical charge transfer element, one readout gate is disposed for each photoelectric converter. In general, one of two vertical transfer electrodes surrounding one photoelectric converter in a plan view also serves as a gate electrode of the readout gate. The vertical transfer electrode serving as the gate electrode is referred to as xe2x80x9cread-cum-transfer electrodexe2x80x9d in this specification.
Each vertical charge transfer element is driven, for example, by four-phase vertical drive signals to transfer electric charge read out from the photoelectric converter to a horizontal charge transfer element.
The horizontal charge transfer element receives the electric charges from the vertical charge transfer elements and transfers the electric charges to an output amplifier. The horizontal charge transfer element is, for example, a CCD of two-phase drive type.
The output amplifier receives the electric charges from the horizontal charge transfer element, converts the charges into image signals (signals voltage), and then outputs the signals to a predetermined circuit.
With spread of the solid-state image pickup device in the world, improvement of performance and reduction in the production cost of the device have been required.
It is therefore an object of the present invention to provide a solid-state image pickup device in a configuration capable of improving the performance and reducing the production cost.
According to one aspect of the present invention, there is provided a solid-state image pickup device, comprising a semiconductor substrate having one surface; a large number of photoelectric converters formed in the one surface of said semiconductor substrate in a matrix pattern including a plurality of rows and a plurality of columns; a vertical charge transfer channel formed in the one surface of said semiconductor substrate adjacent to each column of said photoelectric converters; an electrically insulating layer disposed on the one surface of said semiconductor substrate; and a read-cum-transfer electrode formed on said electrically insulating layer, crossing said vertical charge transfer channels and surrounding photoelectric converters of each of said rows of the photoelectric converters in a plan view.
In the solid-state image pickup device, one vertical transfer electrode (read-cum-transfer electrode) is disposed for each photoelectric converter row. Each photoelectric converter of one photoelectric converter row is surround by the associated read-cum-transfer electrode in a plan view. Therefore, when compared with the solid-state image pickup device of the prior art in which each photoelectric converter is surrounded by two vertical transfer electrodes in a plan view such that one of the vertical transfer electrodes also serves as a read-cum-transfer electrode, it is possible in the above-described solid-state image pickup device to increase the line width of each read-cum-transfer electrode if both solid-state image pickup devices have the same integration degree of photoelectric converters.
Accordingly, the read-cum-transfer electrode can be more easily formed, which simplifies the production of the solid-state image pickup device itself. Therefore, a disadvantage that the degree of integration of photoelectric converters is limited by the line width of the read-cum-transfer electrode under fine manufacturing precision of the prior art rarely occurs. Resultantly, the photoelectric converters can be highly integrated in the solid-state image pickup device. The high degree of integration of the photoelectric converters facilitates improvement of resolution of the solid-state image pickup device.